Next generation wireless communication systems are being designed to provide a variety of internet-based services. To support such services, protocols such as the Session Initiation Protocol (SIP) are being adopted and incorporated into these systems. SIP is a text-based protocol, similar to HTTP and SMTP, for initiating interactive communication sessions between users. Such sessions include voice, video, chat, interactive games, and virtual reality. The Internet Engineering Task Force (IETF) may be contacted for a complete description of the SIP standard.
To incorporate SIP into wireless systems, however, limitations such as the air interface and user mobility must be addressed. For example, SIP uses contact addresses to tie a user's address-of-record to his/her location. The contact addresses are centrally registered with a SIP Registrar using SIP REGISTER messages. However, SIP currently lacks the robustness to efficiently maintain contact addresses for mobile units as they move across service areas, at least in certain wireless implementations of SIP. Therefore, a need exists within the SIP framework for an apparatus and method to effectively and efficiently maintain SIP contact addresses in wireless environments.